Oil base fluids containing hydrophilic tannins

ABSTRACT

The invention provides oil base well drilling and servicing fluids (OBWDSF) containing a hydrophilic tannin to decrease the fluid loss of the OBWDSF. The hydrophilic tannin, which may be sulfited, is preferably selected from the group consisting of quebracho, wattle, and mixtures thereof. The OBWDSF will contain from about 50% to about 100% by volume of a continuous oil phase, and generally will contain up to about 50% by volume of a discontinuous, emulsified aqueous phase. The OBWDSF can also contain other fluid loss control additives other than the hydrophilic tannin, preferably selected from the group consisting of resins, synthetic polymers, Gilsonite, organophilic polyphenolic compounds, and mixtures thereof. The invention also provides a method of decreasing the fluid loss from an OBWDSF which comprises incorporating into the OBWDSF a hydrophilic tannin.

FIELD OF THE INVENTION

The invention relates to oil base drilling and well servicing fluids,and to a method of reducing the loss of fluid therefrom to subterraneanformations contacted by the fluids.

BACKGROUND OF THE INVENTION

In the drilling of wells for oil and gas by the rotary method, it iscommon to use a circulating fluid which is pumped down to the bottom ofthe well through a drill pipe, where the fluid emerges through ports inthe drilling bit. The fluid rises to the surface in the annular spacebetween the drill pipe and the walls of the hole, and at the surface itis treated to remove cuttings and the like to prepare it forrecirculation into the drill pipe. The circulation is substantiallycontinuous while the drill pipe is rotated.

The present invention pertains to oil base drilling fluids or oil basemuds which includes water-in-oil (invert) emulsions as well as oil basefluids containing only small amounts or no emulsified water. Animportant feature of well working fluids of the class described is theirability to resist filtration. In most instances, when they are in actualuse, whether as drilling fluids, packer fluids, fracturing or completionfluids, the well working fluid is in contact with a more or lesspermeable formation, such as, for example, sandstone, sandy shale andthe like, with an effective balance of pressure such that the fluidtends to be forced into the permeable formation. When a well workingfluid is deficient in its ability to resist filtration, then the solidsin the fluid are held back by the permeable formation and build up as afilter cake or sludge on its surfaces, while the liquid per se of thewell working fluid filters into the permeable formation. The filter cakeor sludge thus formed is generally very undesirable. Moreover, the lossof oil to the formation is very expensive, not only because of the costof the oil itself, but also due to the cost of maintaining theproperties and composition of the fluid.

Various additives have been used or suggested for use as fluid lossadditives to prevent or decrease this loss of fluid by filtration fromoil base muds. Some of the first materials used for this purpose wereasphalt and various modified asphaltic materials. The following patentsdisclose various amine derivatives of various polyphenolic compounds foruse as fluid loss control additives (hereinafter sometimes referred toas FLCA) for oil muds: Jordan et al. U.S. Pat. No. 3,168,475; Jordan etal. U.S. Pat. No. 3,281,458; Beasley et al. U.S. Pat. No. 3,379,650;Cowan et al. U.S. Pat. No. 3,232,870; Cowan et al. U.S. Pat. No.3,425,953; Andrews et al. U.S. Pat. No. 3,494,865; Andrews et al. U.S.Pat. No. 3,671,427; Andrews et al. U.S. Pat. No. 3,775,447; Kim U.S.Pat. No. 3,538,071; Kim U.S. Pat. No. 3,671,428; Cowan U.S. Pat. No.4,421,655; Connell et al. U.S. Pat. No. 4,501,672; House U.S. Pat. No.4,569,799; House et al. U.S. Pat. No. 4,597,878; Patel U.S. Pat. Nos.4,637,883 and 4,710,586; Cowan et al. U.S. Pat. Nos. 4,737,295 and4,853,465; Patel U.S. Pat. No. 5,990,050; and Frost European Pat.Application No. 049,484.

Cowan U.S. Pat. No. 4,421,655 discloses organophilic derivatives ofpolyphenolic compounds wherein the polyphenolic compound may be modifiedtannins and the oxidized, sulfonated, and sulfomethylated derivativesthereof, and wherein the organophilic modifier is a polyamine orpolyamidoamine which contain at least two primary, secondary, ortertiary amine groups per molecule selected from the group consistingof:

(I) R—NR′—(C_(x)H_(2x)N′)_(y)H

(II) R—CO—NH—(C_(x)H_(2x)NR′)_(z)H

where 2≦x≦3; y≧1z≧2; R is an aliphatic group containing from 12 to 30carbon atoms; R′ is selected from the group consisting of H and R″—CO,and mixtures thereof; R″ is an aliphatic group containing from 11 to 29carbon atoms; and wherein at least two of the R′ groups are H.

House U.S. Pat. No. 4,569,799 discloses a process of preparingorganophilic derivatives of polyphenolic acids including modifiedtannins and the oxidized, sulfonated, and sulfomethylated derivatives ofthe polyphenolic compounds.

House et al. U.S. Pat. No. 4,597,878 discloses certain organophilicpolyphenolic acid adducts wherein the polyphenolic acid may be derivedfrom tannins such as quebracho, sulfonated quebracho, carboxylatedquebracho, oxidized quebracho, and the like, and wherein theorganophilic modifier is an amide mixture of a polyamide containing nofree amino groups and an amido-amine containing one free amino group permolecule.

Patel et al. U.S. Pat. Nos. 4,637,883 and 4,710,586 disclose alkylquaternary ammonium salts of quebracho.

Cowan et al. U.S. Pat. Nos. 4,737,295 and 4,853,465 discloseorganophilic polyphenolic materials wherein the polyphenolic materialmay be tannins or the oxidized, sulfonated, or sulfomethylatedderivatives thereof, and wherein the organophilic modifier is aphosphatide, preferably lecithin.

Patel U.S. Pat. No. 5,990,050 discloses an invert emulsion fluid whichmay contain a fluid loss control agent such as organophilic tanninsprepared by reacting tannic acid with amides or polyalkylene polyamines.

As noted in the examples in the aforementioned patents, the amount ofthe organic amine or amide compounds reacted with the polymeric phenoliccompounds disclosed is quite high, generally of the order of 30%-100% ormore, based on the weight of the polymeric phenolic compound, althoughamounts from 20% to 200% are disclosed to be useful. Most of these FLCApossess poor dispersibility in well working fluids unless elaborateprocedures are undertaken, such as the addition of a dispersant,heating, agitating under high shear or for extended periods of time,drying under low temperature conditions, flushing, preparation inoleaginous liquids, and the like. Moreover, the amine and amidecompounds are relatively expensive to prepare and/or purchase, and thusthese FLCA are quite expensive to produce.

SUMMARY OF TIHE INVENTION

I have now surprisingly found that the addition of hydrophilic tanninsto oil base well drilling and servicing fluids or muds (hereinaftersometimes referred to as “OBWDSF”) will function as fluid loss controladditives to decrease the loss of fluid therefrom.

Thus it is an object of this invention to provide oil base well drillingand servicing fluids containing a hydrophilic tannin to decrease thefluid loss therefrom.

It is another object of the invention to provide a method of decreasingthe fluid loss of an oil base well drilling and servicing fluid.

These and other objects of this invention will be apparent to oneskilled in the art upon reading this specification and the appendedclaims.

While the invention is susceptible of various modifications andalternative forms, specific embodiments there of will hereinafter bedescribed in detail and shown by way of example. It should beunderstood, however, that it is not intended to limit the invention tothe particular forms disclosed, but, on the contrary, the invention isto cover all modifications and alternatives falling within the spiritand scope of the invention as expressed in the appended claims.

The composition can comprise, consist essentially of, or consist of thestated materials. This method can comprise, consist essentially of, orconsist of the stated steps with the stated materials.

PREFERRED EMBODMENTS OF THE INVENTION

The present invention provides for the addition of hydrophilic tanninsto oil base well drilling and servicing fluids to decrease the loss offluid therefrom. OBWDSF may be prepared by a great variety offormulations with a large number of ingredients, as is well known tothose skilled in the art. Specific formulations depend on the state ofdrilling a well at any particular time, for instance, depending on thedepth, the nature of the strata encountered, and the like. Thecompositions of this invention are directed to and adapted to provideimproved, economical OBWDSF useful under conditions of high temperatureand pressure, such as those encountered in deep wells, where manypreviously proposed and used formulations do not heat age well, andthere is an unacceptable fluid loss noted after operations under suchhigh temperature and high pressure conditions.

THE OBWDSF of the invention will contain a liquid phase which containsfrom 100% oil to about 50% oil as is known in the art. Included areemulsions comprising water-in-oil (w/o) invert emulsions where thecontinuous phase is an oil having the discontinuous water phasedispersed and emulsified therein.

Generally the water phase comprises from about 2% to about 50% by volumeof the combined oleaginous and aqueous phases.

The oil used may be any of the known oleaginous liquids used in the art.Exemplary oils are petroleum oils, such as diesel oil, mineral oils,hydrotreated petroleum oils and the like, synthetic hydrocarbons such asalpha olefins, polyalpha olefins, internally unsaturated olefins, andthe like, and synthetic esters and ethers and the like.

Invert (w/o) base mud formulations intended for use under hightemperature (up to about 250° C.) and high pressure (up to about 172,500kPa (25,000 psi)) conditions normally will contain an oil, a weightingagent, an emulsifier, a gelling agent, salts, and a fluid loss controlagent, as essential ingredients. Water is often added but it may beintroduced from the formations themselves during drilling.

The W/O emulsion OBWDSF contain one or more emulsifiers as is well knownin the art, including alkali and alkaline earth metal salts of fattyacids, rosin acids, tall oil acids, the synthetic emulsifiers such asalkyl aromatic sulfonates, aromatic alkyl sulfonates, long chainsulfates, oxidized tall oils, carboxylated 2-alkyl imidazolines,imidazoline salts, and the like.

Water soluble salts are added to the formulations containing water,normally the brine salts such as sodium chloride, potassium chloride,sodium bromide, calcium chloride most preferably, and the like, normallyin a small amount of water. These salts are added to control the osmoticpressure of the formulations as needed, according to drillingconditions.

Gelling agents include the activated clays, organophilic clays such asbentonite which may have had the surface treated as with quaternaryammonium salts, fatty amines and the like and other gelling orthickening agents such as alkali metal soaps, asphaltic materials,mineral fibers and the like.

Weighting materials include such materials as calcium carbonate,silicates, clays, and the like, but more preferably are the heavierminerals such as the barites, specular hematite, iron ores, siderite,ilmenite, galena, and the like.

These muds normally will be formulated to weigh from greater than 930kg/m³ (no weighting agent) to about 2640 kg/m³ (7.75 to 22 ppg) of mud.Usually the range is from about 1200 kg/m³ to about 2160 kg/m³ (10 to 18 ppg).

The fluid loss control agents useful in the OBWDSF of this inventionare, and indeed are required to be, hydrophilic tannin materials. Thevegetable tannins are well known polyphenols which are extracted fromvarious plants. They can be divided into two categories: catecholtannins, otherwise know as condensed tannins, which are chemicallysimilar to catechol; and pyrogallol tannins, otherwise known ashydrolysable tannins, which are chemically esters of glucose and gallicacid. Exemplary of catechol tannins are extracts from the followingtrees: quebracho, wattle, mimosa, pine, mangrove, eucalyptus, andhemlock. Exemplary of pyrogallol tannins are extracts from the followingtrees: chestnut, sumac, valonia, and myrabolan. Extracts from oak treescontain both kinds of tannins.

The preferred tannins are unmodified water/steam extracted tannins.However, hydrophilic sulfited or sulfomethylated vegetable tannins canbe utilized as the fluid loss additive in OBWDSF. Such sulfited tanninsare well known in the art and are usually prepared by reacting thetannin materials with sulfic acid whereby the extracts acquire SO₃H⁻groups. This transforms them into a more readily water soluble tannin.

The preferred tannins are catechol tannins, most preferably selectedfrom the group consisting of quebracho, wattle, or mixtures thereof.

Commercially available tannins are mixtures of tannins, non-tannin otherextractables, insoluble materials, and of course moisture. For thepurpose of this invention, the hydrophilic tannins shall contain greaterthan about 50% by weight tannin, preferably greater than about 60%tannin.

The concentration of the hydrophilic tannin fluid loss control agents inthe OBWDSF of this invention generally comprises from about 5.7 kg/m³ toabout 85.7 kg/m³ (i.e., about 2 to about 30 ppb), preferably from about14.3 kg/m³ to about 57.1 kg/m³ (5 to 20 ppb). The amount should besufficient to decrease the API HTHP filtrate of the OBWDSF at 121.1° C.(250° F.) or higher temperatures and 3450 kPa (500 psi) by about 40%,preferably at least about 50%, of the fluid loss of the OBWDSF beforeadding the hydrophilic tannin.

The OBWDSF are generally prepared by mixing the emulsifier(s), if used,with the oleaginous liquid, mixing in the aqueous liquid, if used,mixing in the gelling agent (Theological modifier), mixing in thehydrophilic tannin fluid loss control agent, followed by mixing in theweighting material. The OBWDSF may also contain a dispersant for thegelling agent such as a low molecular weight polar organic compound whenthe gelling agent is an organophilic clay. This is generally added afterthe gelling agent is well mixed into the formulation.

The invention also provides OBWDSF which contain known fluid losscontrol agents together with the hydrophilic tannin fluid loss controlagents set forth herein. It has been determined that the fluid loss fromOBWDSF containing known fluid loss control additives can be furthersubstantially decreased by the addition thereto of the hydrophilictannins set forth hereinbefore.

Known fluid loss control, agents/additives used or proposed for use inOBWDSF include various asphaltic materials, resins, synthetic polymers,Gilsonite, and organophilic polyphenolic compounds such as organophiliclignites, organophilic humic acids, organophilic tannins, and the like.Representative of the organophilic polyphenolic compounds are those setforth in the following patents, all of which are incorporated herein byreference: Jordan et al. U.S. Pat. No. 3,168,475; Jordan et al. U.S.Pat. No. 3,281,458; Beasley et al. U.S. Pat. No. 3,379,650; Cowan et al.U.S. Pat. No. 3,232,870; Cowan et al. U.S. Pat. No. 3,425,953; Andrewset al. U.S. Pat. No. 3,494,865; Andrews et al. U.S. Pat. No. 203,671,427; Andrews et al. U.S. Pat. No. 3,775,447; Kim U.S. Pat. No.3,538,071; Kim U.S. Pat. No. 3,671,428; Cowan U.S. Pat. No. 4,421,655;Connell et al. U.S. Pat. No. 4,501,672; House U.S. Pat. No. 4,569,799;House et al. U.S. Pat. No. 4,597,878; Patel U.S. Pat. Nos. 4,637,883 and4,710,586; Cowan et al. U.S. Pat. Nos. 4,737,295 and 4,853,465; PatelU.S. Pat. No. 5,990,050; and Frost European Pat. Application No.049,484.

The concentration of the hydrophilic tannin fluid loss control additivein the OBWDSF containing one or more known fluid loss control additiveswill be an amount sufficient to decrease the fluid loss of the OBWDSF asmeasured by one or more of the industry standard tests as set forth inAPI Recommended Practice RP-13B-1. Generally the concentration ofhydrophilic tannin will be from about 0.285 kg/m³ (0.1 ppb) to about57.1 kg/m³ (20 ppb), preferably from about 0.57 kg/M³ (0.2 ppb) to about42.8 kg/m³ (15 ppb), and most preferably from about 0.71 kg/m³ (0.25ppb) to about 28.5 kg/m³ (10 ppb).

The invention also provides a method of decreasing the fluid loss froman OBWDSF, including OBWDSF containing known fluid loss controladditives, which comprises incorporating into the OBWDSF as disclosedhereinbefore an amount of a hydrophilic tannin to decrease the fluidloss of the OBWDSF. The amount preferably should be sufficient todecrease the API HTHP filtrate of the OBWDSF at 121.1° C. (250° F.) orhigher temperatures by about 40%, preferably at least about 50%, of thefluid loss of the OBWDSF before adding the hydrophilic tannin or knownfluid loss control additive. Generally this will comprise from about0.285 kg/m³ (0.1 ppb) to about 57.1 kg/m³ (20 ppb), preferably fromabout 0.57 kg/m³ (0.2 ppb) to about 42.8 kg/m³ (15 ppb), and mostpreferably from about 0.71 kg/m³ (0.25 ppb) to about 28.5 kg/m³ (10ppb). Exemplary hydrophilic tannins are as hereinbefore set forth.

In order to more completely describe the invention, the followingnon-limiting examples are given. In these examples and thisspecification, the following abbreviations may be used: ppg=pounds pergallon; ppb=pounds per 42 gallon barrel; psi=pounds per square inch;cm³=cubic centimeters; kg/m3=kilogram/cubic meter; kPa=kilopascal;Pa=pascal; ml=milliliters; g=grams; cp=centipoise; rpm=revolutions perminute; sq.ft.=square feet; sec=seconds; min=minutes; W/O=water-in-oil;FLCA=fluid loss control additive; OBWDSF=oil base well drilling andservicing fluid; API HTHP filtrate=American Petroleum institute hightemperature high pressure filtrate as set forth in API RecommendedPractice RP 13B-1.

EXAMPLE 1

An invert w/o base fluid was prepared by mixing together the followingcomponents in the order indicated, with a five minute mixing time aftereach addition and a final ten minute mixing time after the bariteaddition: 7110 ml diesel oil; 150 g CARBO-GEL organophilic clay gellingagent/rheological modifier; 30 ml propylene carbonate organoclaydispersant; 150 ml CARBO-TEQ emulsifier; 240 ml CARBO-MUL emulsifier, 90g lime; 1770 ml of a 30% by weight calcium chloride solution; and 6870 gbarite weighting agent. The CARBO-GEL, CARBO-TEQ, and CARBO-MUL areproducts of Baker Hughes Inteq, Houston, Tex.

To 350 ml (one barrel equivalent) of this base fluid were added theconcentrations of Quebracho TB (obtained from Unitan SA, Buenos Aires,Argentina) and VEN-CHEM 222, an organophilic lignite fluid loss additive(obtainable from Venture Chemicals, Inc., Lafayette, La.) set forth inTable 1 and the fluids were thereafter mixed ten minutes on an Osterizerhigh shear blender. The muds were hot rolled at 176.7° C. (350° F.) and3450 kPa (500 psi) differential pressure for 16 hours, cooled to roomtemperature, mixed ten minutes on an Osterizer blender at high shear,and evaluated for the Fann Rheology, emulsion stability, and HTHP APIfluid loss at 176.7° C. (3500F) and 3450 kPa (500 psi) differentialpressure by the procedures in API Recommended Practice RP 13B-1.

The data obtained are in Table 1. Fluid 1-A and 1-B are for comparisonpurposes only. TABLE 1 Effect of Quebracho on the Fluid Loss of an OilBase Mud Fluid 1-A 1-1 1-2 1-3 1-4 1-B Oil Base Mud, ml 350 350 350 350350 350 Quebracho, g 0 5 10 0.6 1.2 0 VEN-CHEM 222, g 0 0 0 14.4 13.8 15After Hot Rolling for 16 Hours at 176.7° C. (350° F.) Fann Rheology 600rpm (Dial reading) 60 84 80 83 123 85 300 rpm (Dial reading) 31 49 47 4469 46 Plastic Viscosity, cP 29 35 33 39 54 39 Yield Point, Pa (lb/100sq.ft.) 0.96(2) 6.72(14) 6.72(14) 2.4(5)  7.2(15) 3.36(7) 10-sec Gel, Pa(lb/100 sq.ft.) 1.92(4) 5.28(11) 5.76(12) 1.92(4)  1.92(4) 1.44(3)10-min Gel, Pa (lb/100 sq.ft.) 2.88(6) 8.64(18) 8.64(18) 2.4(5) 2.88(6) 2.4(5) Emulsion Stability, v 535 1760 2000+ 509 528 707 Fluid Loss atat 176.7° C. (350° F.), 3450 kPa (500 psi) Fluid Loss, cm³/30 min 84.826.8 25.2 35.6 34.4 47.2 Free Water, cm³ 2.4 0 0 0 0 0 Free Emulsion,cm³ 10.0 0.2 0.2 1.2 0.8 4.0

EXAMPLE 2

An oil base mud was prepared by mixing together 90% by volume of the oilbase mud set forth in Example 1 and 10% by volume diesel oil. To 350 mlof this oil base mud were added and mixed for ten minutes the quantitiesof Ven-Chem 208, an organophilic lignite fluid loss additive obtainablefrom Venture Chemicals, Inc., Lafayette, La., and quebracho set forth inTable 2. The fluids were then hot rolled at 148.9° C. (300° F.) for 16hours, cooled to room temperature, mixed for five minutes on a HamiltonBeach mixer at low shear, and evaluated as in Example 1. The dataobtained are set forth in Table 2. Fluids 2-A and 2-B are for comparisonpurposes only. TABLE 2 Effect of Quebracho and an Organophilic LigniteDerivative on the Fluid Loss of an Oil Base Mud Fluid 2-A 2-B 2-1 2-22-3 Oil Base Mud, ml 350 350 350 350 350 VEN-CHEM 208, g 0 10 9.5 9.08.0 Quebracho, g 0 0 0.5 1.0 2.0 Properties After Hot Rolling at 148.9°C. (300° F.) for 16 hours Farm Rheology 600 rpm (Dial reading) 45 49 5053 60 300 rpm (Dial reading) 23 25 27 28 31 Plastic Viscosity, cP 22 2423 25 29 Yield Point, Pa 0.48(1) 0.48(1) 1.92(4) 1.44(3) 0.96(2) (lb/100sq.ft.) 10-sec Gel, Pa  2.4(5)  2.4(5) 2.88(6) 2.88(6) 2.88(6) (lb/100sq.ft.) 10-min Gel, Pa 2.88(6) 2.88(6) 4.32(9) 3.84(8) 3.84(8) (lb/100sq.ft.) Emulsion Stability, v 379 394 433 513 661 Fluid Loss at 148.9°C. (300° F.), 3450 kPa (500 psi) Fluid Loss, cm³/30 min 23.2 13.6 6.87.2 7.2 Free Water, cm³ 0 0 0 0 0 Free Emulsion, cm³ 0.2 0.2 0 0 0

EXAMPLE 3

The API fluid loss at 690 kPa (100 psi) and room temperature wasdetermined for various oils containing the quantities of Ven-Chem 222,an organophilic lignite fluid loss control additive obtainable fromVenture Chemicals, Inc., Lafayette, La., and quebracho set forth inTable 3. The fluids were mixed for ten minutes on a Hamilton BeachMultimixer. The oils evaluated were diesel oil, BioBase, an internalolefim obtainable from Shrieve Chemical Company, Houston, Tex. and VASSALP-90, obtainable from Vassa, Estado Falcon, Venezuela

EXAMPLE 4

The procedures in Example 2 were repeated except that the concentrationof the hydrophilic tannins evaluated as fluid loss control additiveswere 14.2 kg/m³, 28.5 kg/m³, or 42.8 kg/m³ (5, 10, or 15 ppb). TABLE 3Effect of Quebracho and an Organophilic Lignite Derivative on the FluidLoss of Various Oils Fluid 3-1 3-2 3-3 3-4 3-5 Diesel Oil, ml 350 350350 0 0 BioBase, ml 0 0 0 350 0 VASSA LP-90, ml 0 0 0 0 350 VEN-CHEM222, g 4.8 14.4 13.8 14.4 14.4 Quebracho, g 0.2 0.6 1.2 0.6 0.6 APIFluid Loss at 690 kPa (100 psi) cm³/30 min. 10 4 3.5 42 17

TABLE 4 Fluid 4-A 4-1 4-2 4-3 4-4 4-5 Oil Base Mud, ml 350 350 350 350350 350 Quebracho, g 0 5 10 15 0 0 Sulfited Quebracho, g 0 0 0 0 10 0Wattle Extract, g 0 0 0 0 0 10 Properties After Hot Rolling for 16 Hoursat 148.9° C. (300° F.) Farm Rheology 600 rpm (Dial reading) 48 65 67 8359 55 300 rpm (Dial reading) 27 34 37 47 30 29 Plastic Viscosity, cP 2131 30 36 29 26 Yield Point, Pa (lb/100 sq.ft.) 2.88(6) 1.44(3) 3.36(7) 5.28(22) 0.48(1) 1.44(3) 10-sec Gel, Pa (lb/100 sq.ft.) 1.92(4)  2.4(5)3.36(7) 3.36(7) 2.88(6)  2.4(5) 10-min Gel, Pa (lb/100 sq.ft.) 3.36(7)3.84(8) 3.84(8)  4.8(10)  4.8(10) 3.84(8) Emulsion Stability, v 337 10391029 997 841 612 Fluid Loss at 176.7° C. (350° F.), 3450 kPa (500 psi)Fluid Loss, ml/30 min 22.4 9.6 9.2 9.2 11.2 8.0 Free Water, ml 0.2 0 0 00 0 Free emulsion, ml 0.2 0 0 0 0 0

1. An oil base well drilling and servicing fluid which comprises an oilcontinuous phase containing a hydrophilic tannin therein in an amount todecrease the fluid loss therefrom.
 2. The oil base well drilling andservicing fluid of claim 1 wherein the hydrophilic tannin is selectedfrom the group consisting of quebracho extract, wattle extract, andmixtures thereof.
 3. The oil base well drilling and servicing fluid ofclaim 2 wherein the hydrophilic tannin has been sulfited.
 4. The oilbase well drilling and servicing fluid of claim 1 which additionallycontains a fluid loss control additive other than the hydrophilictannin.
 5. The oil base well drilling and servicing fluid of claim 4wherein the additional fluid loss control additive is selected from thegroup consisting of resins, synthetic polymers, Gilsonite, organophilicpolyphenolic compounds, and mixtures thereof.
 6. The oil base welldrilling and servicing fluid of claim 1, 2, 3, 4, or 5 whichadditionally contains an aqueous phase emulsified into the continuousoil phase, one or more emulsiflers, a rheological modifier, and aweighting agent.
 7. The oil base well drilling and servicing fluid ofclaim 6 wherein the aqueous phase comprises from about 2% to about 50%by volume of the combined liquid phase of the oil base well drilling andservicing fluid.
 8. A method of decreasing the fluid loss from an oilbase well drilling and servicing fluid which comprises incorporatinginto the oil base well drilling and servicing fluid a hydrophilictannin.
 9. The method of claim 8 wherein the hydrophilic tannin isselected from the group consisting of quebracho extract, wattle extract,and mixtures thereof.
 10. The method of claim 9 the hydrophilic tanninhas been sulfited.
 11. The method of claim 8 wherein the oil base welldrilling and servicing fluid additionally contains a fluid loss controladditive other than the hydrophilic tannin.
 12. The method of claim 11wherein the additional fluid loss control additive is selected from thegroup consisting of resins, synthetic polymers, Gilsonite, organophilicpolyphenolic compounds, and mixtures thereof.
 13. The method of claim 8,9, 10, 11, or 12 wherein the oil base well drilling and servicing fluidadditionally contains an aqueous phase emulsified into the continuousoil phase, one or more emulsifiers, a Theological modifier, and aweighting agent.
 14. The method of claim 13 wherein the aqueous phasecomprises from about 2% to about 50% by volume of the combined liquidphases of the oil base well drilling and servicing fluid.